From my understanding a star is only visible if the light has had enough time to travel to Earth.
The Egyptians, Greeks, Mayans, were all very into documenting the night sky.
Are there any stars in the sky tonight that ancient people never saw?
Are there any stars that we can no longer see that were documented back then?
I know 4,000 years is nothing in astronomy, but maybe???
I’m talking about stars that are visible using the same technology as the ancients.
You mean eyeballs?
Stars far enough away that light from them only arrived here recently, would be so far away they would not be visible to the naked eye (or most anything else).
Any new stars you can see now that you couldn’t 4000 years ago would likely just be visible due to relative motion. A star previously occluded by another so not visible, may now be out from behind. There are also Nova, or other stars that changed brightness enough to be visible now when they weren’t before.
There are ‘star-forming’ regions that have been identified in the local galaxies, so they are creating new stars.
There are stars exploding into supernovas or just dying out all the time.
Are these processes approximately? I don’t know; maybe nobody knows – that would mean something about the state of the universe & fundamental physics, right?
Also, the universe is expanding. Some stars the ancients saw might now be too far away for us to see (except that we have much better equipment now). Indeed, some of the stars we see now may not be there anymore – since the time their starlight started travelling toward us, they have died out.
Real interesting question here.
Four thousand years ago, they didn’t have any instruments other than the Mark 1 eyeball. Considering light polution, there’s far fewer stars naked-eye stars.
Ignoring light polution, the number has not changed significantly.
I can only think of one star that is sort of not visible that used to be. Pleione, one of the Pleiades, is a variable star that may have been more visible to the ancients. She’s the “missing sister” in various mythologies. Pleione is still 5th magnitude, which should be visible, but she’s close to Atlas, a third magnitude star, making her difficult to see. Some people can see her from a dark sky.
Novas and supernovas are only visible for short periods of time. For example, Sanduleak -69° 202, the progenitor star to Supernova 1987A, was not visible before that event and is not visible now.
Because of precession, the stars visible at a given location will change somewhat over the centuries, but they’re all going to be visible from some place. For example, the constellation Centaurus was visible to the ancient Greeks (or at least to Ptolemy, who was living in Alexandria, Egypt) but is not visible from that part of the world today. Some other constellation(s) are now visible in another part of the sky as replacement, although I don’t know which.
Over a great deal of time there should gradually be fewer visible stars. Most of the well known stars that we can see are many times more luminous than the sun; they are larger in mass as well, but not to the same extent. In short, they trade longevity for a short lifetime of radiating enormous amounts of light. Bright supergiants like Betelgeuse and Rigel are in their end stages and will turn nova about twenty minutes from now, astronomically speaking. Bright main sequence stars like Sirius aren’t quite at death’s door yet, but their lifespan is measured in millions or a few hundreds of millions of years in contrast to the Sun, which is less than halfway through its estimated 10B year lifespan.
The longest lived stars of all are the red dwarfs, and in the far future there will come a time when they are the only stars left–and not a single one would be visible from Earth, assuming it could still possibly exist. Most of the stars nearest to us now are red dwarfs, and few if any of those are visible to the naked eye.
What about the progenitor of the Crab Nebula? Light from that supernova reached Earth in the 1054AD. Would the star have been visible to the naked eye before that date? Anyone know?
IANAAP, but since the universe is expanding at a rate faster than the speed of light, I don’t believe it’s possible for us to see light (with naked eye) from a long existing star that the ancients could not see. The opposite could be true, however. The universe is getting darker, not brighter.
It’s as though our extra-galactic neighbors can’t get away from us fast enough. Are we that obnoxious?
Today, the Crab Nebula is visible only with binoculars. Before it exploded it was about 6500 light-years away. I know almost nothing about stars, but explain why I suspect that few, if any stars at that distance would be visible:
I’d downloaded a database of stars, 6300 of which are of apparent magnitude 6.2 or brighter. Of these visible stars, the database provides distance estimates for all but 130.
Among the visible stars with distance estimates, the yellow supergiant (F6Ib) 35 Cygni at 3300 light-years distance (half the distance to Crab Nebula) is the most distant.
Among the 130 visible stars in that database for which no distance estimate is offered, the one with brightest apparent magnitude is Beta Phoenicis, a visual binary (G8III + G8III) whose distance might be 200 light-years.
Not so. Deneb, the head of Cygnus the swan, is a bright star and is 2500 light years away. Eta Carinae, a naked eye star visible in the southern hemisphere, is 7500 light years away.
This is a common misconception: where there is a limited absolute viewing distance (the technical term is ‘particle horizon’), new objects are always appearing in the observable universe. This is a fundamental feature of such models, assuming the Universe has an open topology. This of course ignores practical limitations to the observation of distance objects.
The furthest galaxy currently observed is 13.39 bly away in light travel distance. Assuming an age of the Universe of 13.77 billion years, this means it entered our observable Universe 380 million years ago when our tetrapod ancestors were making their first tentative steps on land.
Although this does happen occasionally, it’s only with stars that are orbiting each other, extremely closely together, and hence with an extremely short period. Eight hours is a typical number. And all eclipsing binaries are too faint to be seen with the naked eye, and even through a telescope, it’s almost always impossible to resolve them as two separate stars: We only know that they’re eclipsing binaries because of the change in total brightness.
For stars which aren’t orbiting each other, the size of the star is so small compared to the distances between them that what you’re describing is impossible.
It would be a bit surprising if they weren’t at least approximately equal: If they aren’t, then the number of stars in the Universe is changing, in a direction which would bring them closer to being equal (since a larger number of stars would mean more stars dying, but would not mean more being born).
And to anyone who mentioned the expansion of the Universe, that’s completely irrelevant here. That only shows up on scales much larger than any individual galaxy, and all the stars we see with the naked eye are within our own Galaxy (there are a few other galaxies which are, as a whole, also visible to the naked eye, but they’re all part of our Local Group, in orbit around each other and the Milky Way, so they’re still too close for expansion to be relevant).
I’ll have you know my tetrapod ancestors took their first steps bravely and without reservation!
Actually there are at least four visible to the naked eye. I knew about Algol off the top of my head; it’s relatively famous for being an eclipsing binary. This page includes four. I couldn’t find any others with a casual search.
Huh, I thought that Algol was a pulsating variable, not an eclipser.
But they were visible to the ancients as well.
The question was, are there stars that were not visible to the ancients, that are now.
If you’re talking just about with the naked eye I think the ancients could see more than you can with the naked eye in the middle of the city because it would have been so much darker. Obviously with technology we can see more now. I don’t think there are any new stars visible to the naked eye in the last 4k years though.
The question can’t be answered without considering the proper motion of stars and the motions of galaxies in our local group. Their gravitational attraction overwhelms expansion, so one day our local group will be all we can see, with everything else receded so far away it will be outside our ‘light bubble’ and permanently invisible to us - along with most evidence of the evolution of the universe. But that’s a LONG way into the future.
Before that happens, but still a Long way in the future (like 10 times the current age of the universe), all 54 galaxies in our local group will merge into one gigantic elliptical galaxy. That should result in a lot more stars visible in the sky (but maybe not - it will be REALLY big, and it’s not clear if the density of stars near enough to us to be seen with the naked eye will be larger or smaller). Of course, our sun will be long gone by then.
In the shorter time frame (‘shorter’ being 4 billion years or so), the Andromeda galaxy will collide with ours. So for a long time before that happens, Andromeda will get brighter and bigger in the sky. It’s already visible with the naked eye in a really dark sky and much larger than the moon. One day it will be spectacular and fill the sky with billions of stars we can’t resolve today.
Somewhat before that happens, the gravitational influence of the other galaxy will start to disturb gas clouds in the Milky Way, leading to bright new star forming regions. So there may be an increase in stars visible in our galaxy say a billion years before the actual collision.
Then there is the proper motion of other stars near us. At large scales, the galaxy looks like a fairly ordered spiral with everything moving together. But if you zoom in the spiral arm we are in, you will see a lot of motion in all directions between the stars. Some are moving towards us, some moving away. This will eventually change the number of stars that you can see with the naked eye, since most naked eye stars are fairly local to us.
For example, Gliese 710 is 64 light years away right now, but in about a million and a half years will pass so close to us it will go through the Oort cloud. This could have interesting effects, like dislodging a rain of comets on the inner solar system. It will also be very bright.
In general, I would say that small changes in visible star count will happen over periods of thousands of years, but it won’t really change the perception of the number of stars in the sky and will be of interest mainly to astronomers. The big changes won’t happen for billions of years.
Specific stars? Yes. There are hundreds of nearby stars whose proper motion is bringing them closer to us, and hundreds moving away. The ones moving closer are getting brighter, and it’s almost certain that there are some bright enough to be seen today that could not be seen thousands of years ago. And some that were visible then that no longer are.
Stars don’t move that far in only 4000 years, at least not compared with the total distance to that star. Some marginally visible stars may become a little bit less visible and some a smidgen more visible, but things like the darkness of the observing site and the turbulance of the sky will be much bigger factors about whether the star is visible or not.